Soundproofing restraining system

ABSTRACT

Soundproofing, restraining systems including at least one transparent acrylic glass panel that contains at least one embedded metal cable. A layer of plastic is provided, at least partially, between the surface of the metal cable and the transparent acrylic glass matrix. The restraining systems can be used in particular as noise barriers.

The present invention relates to sound-deadening retention systems, andalso to their use as a noise barrier.

Transparent soundproofing units can be composed of transparent syntheticpolymer sheets, which can be bonded to suitable fastening equipment togive soundproofing barriers. Transparent soundproofing units areincreasingly used in areas where the noise-barrier installations have tobe as inconspicuous as possible. This requirement applies particularlyon bridges and towards the centres of built-up areas. These transparentnoise barriers are in particular manufactured from polymethylmethacrylate (PMMA) or from PMMA-based moulding compositions, since thismaterial has excellent transparency and optical properties, and alsogives good sound deadening with good physicomechanical properties (stoneimpact resistance). DE-G 90 10 087.5 discloses the possibility ofinserting threads of synthetic polymer into transparent syntheticpolymer sheets. While the sheets constitute a single soundproofing unit,in the event of sheet fracture the threads of synthetic polymer retainthe separate fragments and prevent them from falling away.

EP-A-0 559 075 moreover describes acrylic soundproofing units whichcomprise embedded spirals to prevent splintering of the noise barrier onfracture. The spaces within the spirals, which comprise steel springs,are in at least part of their cross section hollow or filled with adeformable medium, such as oil. The intention of these measures is thatfragments arising on impact are held together. For the teaching ofEP-A-0 559 075 it is significant that the spiral springs have a highdegree of movement available within the synthetic polymer matrix. Thishigh degree of available movement is ensured by the above-mentionedcavities.

EP-A-0 559 075 states in this connection that steel springs have a highmodulus of elasticity. This means that even at low strain the tensileforces increase so rapidly that the ultimate tensile strength can beexceeded when the sheets fracture. The cavities described in EP-A-0 559075 can be created by displacers which are removed after production ofthe sheets. In EP-A-0 559 075 there are no indications of a syntheticpolymer layer arranged between the steel springs and the syntheticpolymer matrix.

A particular disadvantage of an article in accordance with EP-A-0 559075 is the high manufacturing cost of these acrylic sheets. For example,a displacer included in the casting process must first be carefullyremoved from the sheet before the resultant cavity can be filled, forexample with oil. In addition, weathering generally causes rapiddegradation of the oil. This can lead to impairment of the appearance ofthe soundproofing barrier. If the cavities are not filled with oil thereis the risk of water penetration, and in particular in winter water candamage the barrier. If water which has penetrated the cavities freezesthe result can be irreparable damage to the barrier.

In addition, in the abovementioned soundproofing barriers it is merelysplintering of the noise barrier which is prevented. If a vehicleimpacts a known acrylic sheet at high speed it generally punctures thenoise barrier. It has to be borne in mind here that the high degree ofmovement available to the spiral springs can cause them to separate fromthe material. EP-A-0 559 075 describes no additional devices which couldprevent separation from the material. However, devices of this typewould have to have direct connection to the steel wires, creating therisk that water penetrates the cavities. Devices of this type wouldmoreover have to be composed of high-specification metal and be ofcomplicated design. A device of this type would therefore be complicatedand very expensive.

This fracture behaviour of the noise barrier is not acceptable for manyapplications. In particular on bridges or in multi-storey car parks,puncture of the barrier on impact has to be avoided.

Bearing in mind the disadvantages described above and associated with adesign based on EP-A-0 559 075, the prior art achieves this aim throughadditional retention systems, but these destroy the visual advantage,described above, of acrylic sheets over noise barriers composed ofconcrete. In addition, these additional systems imply high installationand maintenance costs.

In the light of the prior art stated and discussed herein, it was anobject of the present invention to provide a sound-deadening retentionsystem which has particularly low installation and maintenance costs.

Another object of the present invention was to provide an aestheticallyattractive sound-deadening retention system which has particularly lowproduction cost.

Another object on which the invention was based was to provide aretention system which does not impair, or impairs only to a very slightextent, the good aesthetic impression given by an acrylic noise barrier.

Another objective of the present invention was to providesound-deadening retention systems which have particularly highweathering resistance.

The sound-deadening retention systems described in claim 1 achieve theseobjects, and also other objects which, although they are notspecifically mentioned, are obvious or necessary consequences of thecircumstances discussed herein.

Useful modifications of the retention systems of the invention areprotected by the subclaims dependent on claim 1.

Claim 17 achieves the object set in relation to a use of the retentionsystems.

A transparent acrylic sheet which comprises at least one embedded metalcable, where between the surface of the metal and the transparentacrylic matrix there is, at least in part, a synthetic polymer layer,provides a surprising and not readily foreseeable method of providing asound-deadening retention system with particularly low installation andmaintenance cost. It has to be borne in mind here that an additionalinstallation step becomes unnecessary, and unlike conventional retentionsystems, the noise barrier is practically maintenance-free.

The noise barriers of the present invention can moreover be producedsimply and at low cost. The retention system integrated into the acrylicsheets has particularly high weathering resistance, since it is entirelysurrounded by synthetic polymer.

For the purposes of the present invention, the term retention systemmeans a device suitable for preventing an impacting article, such as avehicle, from puncturing the device. In one preferred embodiment, aretention system of the invention can prevent an article impacting thesystem perpendicularly and having a velocity of at least 5, preferablyat least 7, metres per second, and an energy of at least 5 000 joules,preferably at least 7 000 joules, from puncturing the system, thuseffectively retaining the same.

The transparent acrylic sheets are known per se to the person skilled inthe art. These sheets may be cast from methyl methacrylate syrup, forexample. Typical sheet thicknesses are from 4 to 40 mm, preferably from12 to 25 mm. The sheets are usually manufactured in a size of from 1.5m×1 m to 2 m×3 m, and larger or smaller embodiments are also possiblefor specific applications.

The sheets are usually substantially transparent, preferably colourlessor with a pale tint, e.g. smoke brown. The colourless, glass-cleartransparent synthetic polymer sheets usually have a transmittance of atleast 70%, and a transmittance of from 90 to 95% is advantageous. Tintedembodiments usually have a transmittance of from 45 to 75%, usually from50 to 60%.

Any polymeric material may be used to produce the synthetic polymerlayer, but the synthetic polymer layer has to be distinguishable fromthe acrylic matrix which surrounds the synthetic polymer layer.Preference is given to synthetic polymers which are incompatible withthe acrylic material. Particularly suitable materials for producing thesynthetic polymer layer are therefore polyamides, polyesters and/orpolypropylene. The thickness of the synthetic polymer layer may varywithin a wide range. However, the thickness is generally in the rangefrom 50 μm to 1 mm, preferably from 100 μm to 500 μm, although noresultant restriction is intended.

For the purposes of the present invention, the term metal cable is to beinterpreted widely. The metal cable may therefore be a monofilamentwire. The cable may also be obtained by twisting two or more wires,making the metal cable a polyfilament.

The strength of the metal cable depends, inter alia, on the intended useof the noise barrier, and also on the number of cables present in thepossible impact zone.

The metal cable generally has an ultimate tensile strength in the rangefrom 1 000 N to 100 000 N, preferably from 1 500 N to 10 000 N, amodulus of elasticity in the range from 50 000 N/mm² to 1 000 000 N/mm²,preferably from 80 000 N/mm² to 500 000 N/mm², and a tensile strength inthe range from 50 000 N/mm² to 1 000 000 N/mm², preferably from 80 000N/mm² to 500 000 N/mm², but no resultant restriction is intended. Themechanical properties are determined in accordance with the usualstandards as set out and described by known institutes. These includethe standards DIN EN 10002-1 and DIN 53 423.

The metal of which the cables are composed is not of criticalsignificance. According to one particular embodiment of the presentinvention, the metal should have not only good mechanical properties butalso high weathering resistance. Particularly suitable materials aretherefore metal alloys which encompass iron, for example steel, which ina preferred embodiment is preferably stainless. The coefficient ofthermal expansion of the metal should moreover be in the region of thatof the synthetic polymer matrix, in order to avoid stresses attributableto temperature variations.

The cross sectional shape of the metal cable is not significant for thepresent invention. Use may therefore be made of cables with round, oval,rectangular or square cross section.

Depending on the desired strength of the metal, on the number of threadsper unit area and the intended use, the cross-sectional area of themetal cable can vary over a wide range. The cross sectional area isgenerally, however, in the range from 0.3 mm² to 20 mm², from 0.8 mm² to7 mm². A metal cable with a round cross section therefore has anapproximate diameter in the range from 0.6 to 5 mm, preferably from 1 to3 mm, but there is no intention that the invention be restrictedthereto.

In one particular embodiment, the synthetic polymer layer has beenapplied to the metal cable. The production of this particular embodimentis particularly simple, since synthetic-polymer-coated metal cablesmerely have to be introduced in a known manner into a casting mould.

According to the invention, between the metal cable and the acrylicmatrix there is, at least in part, a synthetic polymer layer. There canbe a wide range of variation of the proportion covered by the syntheticpolymer layer on the surface of the metal cable. At least 80%,preferably at least 90%, of the surface of the metal cable is generallycovered. For the purposes of the invention, the interpretation of theterm covering is as follows: that surface of the synthetic polymer layerwhich faces towards the metal cable is calculated to amount to at least80% and, respectively, at least 90% of the surface of the metal cableexcluding indentations resulting from cross-sectional shape, and 100%here represents complete sheathing of the metal cable. In accordancewith the embodiment described above, therefore, the metal cable has notmore than 20% of its surface, preferably not more than 10% of itssurface, in contact with the acrylic matrix. In one particularembodiment, a synthetic polymer layer completely surrounds or sheathsthe metal cable.

The forces for extraction of the steel wire from the acrylic matrix aregenerally greater than 50 N, preferably greater than 100 N, but noresultant restriction is intended. This force is determined in a knownmanner by applying forces to load free-lying metal cable. The minimumforce needed to pull the cable out from the material is defined as theextraction force.

Depending on the intended use, the number of metal cables present in theacrylic sheet can vary over a wide range. For example, one metal cableof particularly high ultimate tensile strength oriented horizontally cansuffice. However, two or more cables are generally inserted, optionallyarranged parallel to one another. If the arrangement of the cables ishorizontal, however, preference is then given to arrangements whichprovide non-uniform distribution of the cables, more cables beingpresent towards the ground than at the upper margin of the sheet.

The arrangement of the metal cables may be in a straight line parallelto the surface of the acrylic matrix, or involve a deviation from atheoretical straight line through the ends of the cables.

This positioning of the metal cables with some degree of “sag” in theacrylic matrix leads under certain circumstances to more advantageousbehaviour when sheets of the invention suitable as a noise barrier aresubject to the relevant tests known to the person skilled in the artfrom the appropriate standards. For the purposes of the invention,maximum deviation means the greatest distance of the cable from atheoretical line drawn between the two ends of the respective cable.

The maximum deviation of a cable positioned with sag is generally atleast 1 mm, preferably at least 3 mm and particularly preferably atleast 5 mm.

This maximum deviation must not be permitted to cause the cable to lieoutside the sheet: for the purposes of the invention actual embedding ofthe metal cables always has to be ensured. The maximum deviation, whichfor simplicity is also termed the deflection of the metal cable, cannottherefore be greater than the thickness of the sheet minus the diameterof the cable.

According to one embodiment of the invention, the deviation of the metalcable may be substantially perpendicular to the plane of the sheet. Anexample of a method of achieving this shape of the embedded cables is touse the action of gravity when embedding the cables into an acrylicmoulding composition for the purposes of casting in a horizontalcell-casting process.

As an alternative to this embodiment, it can also be preferable for thedeviation of the metal cables to be substantially parallel to the planeof the sheet. One method which inevitably gives rise to this type ofembodiment of filament arrangement is casting of the sheets by what isknown as the Rostero process. With the vertical cells usual according tothat process, the action of gravity causes the cables to bend or hangparallel to the plane of the sheet.

Another advantageous embodiment of the sheets of the present inventionprovides a sheet comprising cables whose deviation is substantiallyperpendicular to the plane of the sheet and comprising cables whosedeviation is substantially parallel to the plane of the sheet. Anexample of a method for obtaining this type of arrangement of the metalcables is to use two cables of different length so that one cable has adeviation parallel to the surface of the sheet, and the other cable hasa deviation perpendicular to the plane of the sheet.

It is also possible for two 15 mm sheets with perpendicular and,respectively, parallel deviation with respect to the surface of thesheet to be adhesive-bonded together to give a sheet of thickness 30 mm,thus obtaining a sheet of the invention.

A particular case involves a metal cable embedded by rolling, withparticularly advantageous fracture behaviour.

Depending on the procedure and on the production of the sheets of theinvention, almost any desired orientation of the metal cables in thepolymer matrix is therefore possible. For example, alongside aperpendicular or parallel arrangement with respect to the plane of thesheet it is also possible to achieve any desired degree of deviationbetween these boundaries.

According to the invention, the cables may run substantially parallel toone of the surfaces of the sheet.

The invention also permits the embedding into the polymer matrix ofcables which do not run parallel to a surface but which, for example,have been embedded running perpendicularly.

This means that in relation to the first variant, in one particularlyadvantageous embodiment the cable ends of at least one cable are atsubstantially the same distance from one surface in the plane of thesheet and/or from one of the edges of the sheet. As long as theabovementioned condition has been fulfilled, the embedded cables aresubstantially parallel to one surface in the plane of the sheet and/orto one of the edges of the sheet.

As an alternative to this, in relation to the second variant, there canalso be preferred embodiments in which the distance of the cable ends ofat least one cable from one surface in the plane of the sheet and/orfrom one of the edges of the sheet is different.

Examples are used below, with reference to the attached figures, toprovide a more detailed illustration of the particular embodimentsdescribed above of the present invention.

FIG. 1 shows a cross section through a soundproofing unit with a firstcable arrangement;

FIG. 2 shows a cross section through a soundproofing unit with a secondcable arrangement;

FIG. 3 shows a cross section through a soundproofing unit with a thirdcable arrangement;

FIG. 4 a, b show a cross section through a soundproofing unit with afourth cable arrangement, and also a section along the line A-A in 4 a;

FIG. 5 a, b show a cross section through a soundproofing unit with afifth cable arrangement, and also a section along the line A-A in 5 a;

FIG. 6 a, b shows a cross section through a soundproofing unit with asixth cable arrangement, and also a section along the line A-A in 6 a;

FIG. 7 shows a cross section through a soundproofing unit with a seventhcable arrangement;

FIG. 8 shows a cross section through a soundproofing unit with an eighthcable arrangement;

FIG. 9 shows a cross section through a soundproofing unit with a ninthcable arrangement; and

FIG. 10 shows a perspective plan view of a sheet produced by the Rosteroprocess with embedded metal cables whose deviation is perpendicular tothe plane of the sheet.

The figures have been simplified by not showing the synthetic polymerlayers provided between the acrylic matrix and the metal cables.

In FIG. 1, the reference numeral 1 indicates an acrylic sheet withembedded metal cables provided at least to some extent with a syntheticpolymer sheath. Reference numeral 2 indicates the polymer matrix, whilereference numeral 3 indicates a metal cable. 4 and 4′ identify thebeginning and end of the cable. The distances of the beginning of thecable and end of the cable from the surface 5 are identical, as are thedistances of the beginning of the cable and the end of the cable fromthe surface 6. It can be seen that halfway between the beginning 4 ofthe cable and the end 4′ of the cable the filament 3 has a maximumdeviation, i.e. departure from the theoretical connecting line, i.e.from the straight line between 4 and 4′.

In FIG. 2, another embodiment can be seen, and although this again showsan identical distance of 4 and 4′ from the surface 5 and from thesurface 6, the distances to the two surfaces 5 and 6 differ from oneanother. The cable shown is therefore not central, and is therefore notsymmetrical, but instead the cable shown has been embeddedasymmetrically.

The embodiment shown in FIG. 3 is a cable embedded “obliquely” into apolymer matrix and at least to some extent provided with a syntheticpolymer sheath. A particular feature provided here is that the distanceof the filament ends 4 and 4′ of a filament from one and the samesurface in the plane of the sheet (surface 5 or 6) is different.

FIG. 4 provides evidence of another embodiment of the cablearrangements. This involves two visible embedded, at least to someextent synthetic-polymer-sheathed cables 3 and 3′ which have analternating arrangement. This means that the “sag” or “deviation” of onecable 3′ is more marked than that of the other visible cable 3illustrated. The two cables 3 and 3′ illustrated may, of course,represent a series of filaments in the sheet. It is also clear that oneof the cables may also have been embedded without any significantdeviation or without any significant sag, while the second cableillustrated (reference 3′) has relatively marked deviation from thenormal lie. In FIG. 4 b, the position of the cables 3 and 3′ is furtherillustrated via a section along the line A-A in FIG. 4 a.

FIG. 5 shows yet another variant of the soundproofing units. Thisinvolves a multilayer arrangement of mutually superposed cables. Thesemay have an arrangement with a directly mutually superposed sag, but theinvention also includes multilayer embodiments with offset cables.

Like the preceding FIGS. 4 a, b and 5 a, b, FIG. 6 also shows not only across section but also a plan view of another embodiment of theinventive arrangement of metal cables provided at least to some extentwith a synthetic polymer layer. It is clear from FIGS. 6 a, b that anetwork arrangement of sagging filaments is also possible.

The maximum deflection of a cable provided at least to some extent witha synthetic polymer surface is clear from the cross section of anotherembodiment in FIG. 7. It is not more than the thickness of the sheetminus the thickness of the cable.

FIG. 8 gives another embodiment. It shows the cross section of anembodiment in which the deviation varies from filament to filament. Forexample, at a sheet thickness of about 20 mm the maximum deviationincreases from 1 mm for the highest-tension cable to 19 mm for the cablewith maximum deflection.

Another possible embodiment within the scope of the invention is clearfrom FIG. 9. A corrugated arrangement of the cable can be seen in crosssection.

Finally, the embodiment depicted in FIG. 10 is one in which thearrangement of the embedded metal cable is such that their sag ormaximum deviation runs parallel to the plane of the sheet. As indicatedabove, this type of arrangement of the filaments is readily obtainablefrom the Rostero process, for example.

According to another embodiment of the present invention, acrylic sheetsalso encompass filaments composed of synthetic polymer. This measure canimprove splinter retention to an unexpectedly high extent.

The embedded threads composed of synthetic polymer are usually composedof a synthetic polymer incompatible with the polymer matrix of theacrylic sheet. Polyamide threads or polypropylene threads are suitable,for example. Preference is given to monofil threads, i.e. monofilaments.The threads usually run horizontally in the synthetic polymer sheet,since the sheets are clamped laterally. Coherence in the event offracture is then particularly good. The threads are generally laidparallel to one another. If desired or required, two layers of threadscan be introduced into the sheet, and these then preferably run in twodirections, an angle of 90° between threads of different layers beingparticularly advantageous. This type of embodiment has the externalappearance of a woven mesh.

However, it is also possible to embed the threads in such a way that atleast one of the embedded threads has a maximum deviation of 1 mm ormore from a theoretical straight line through the ends of the thread.This positioning of the metal cables with some degree of sag in theacrylic matrix leads under certain circumstances to more advantageousbehaviour when sheets of the invention suitable as a noise barrier aresubjected to the relevant tests known to the person skilled in the artfrom the appropriate standards. Reference is made here to thepositioning of the steel cables in an arrangement with sag.

The orientation of the synthetic polymer threads may, inter alia, beparallel to the metal filaments. In one preferred embodiment, thethreads composed of synthetic polymer and the metal cables form an anglein the range from 40° to 90°.

The sheets of the invention are used as a noise barrier, for example inmulti-storey car parks, or else towards the centre of built-up areas, onbridges.

The invention is illustrated in more detail below by an example and acomparative example, but there is no intention that the invention berestricted to this example.

EXAMPLE 1

To produce an acrylic sheet, a cell was formed from 2×3 m sheets ofpolished silicate glass with the aid of a peripheral 20 mm gasket.Monofil polyamide threads with a diameter of 2 mm were clamped parallelto one another into this cell, each at a separation of 30 mm. At anangle of 90° to the polyamide threads, polyamide-coated steel cableswere inserted. The steel cables had a modulus of elasticity of 10,000kg/mm², a tensile strength of 170 kg and an ultimate tensile strength of230 kg.

The cell was then filled with methyl methacrylate syrup which compriseda free-radical-generating initiator. The filled cell was placed in awater bath and the syrup was cured by introduction of heat to give asheet of high-molecular-weight polymethyl methacrylate. The chamber washorizontal during polymerisation. After demoulding this gave a castacrylic sheet of dimensions about 2×3 m and thickness 20 mm, withembedded polyamide-coated steel cables and polyamide threads. The forcesfor extraction of the steel wire from the matrix were greater than 100N.

The resultant sheet was subjected to a pendulum test. The principle ofcarrying out this test is that a 300 kg steel weight is raised to 2.64metres and used to break the sheet. The weight is composed of twobutt-welded cone frusta. The impact velocity was 7.2 m per second, andthe energy was 7776 joules.

Three sides of the sheets of dimensions 2×3 m were installed into asteel frame structure. At each corner of the sheet there is a hole at adistance of 15 cm serving to receive the fixing system, i.e. a steelcable secured to the frame structure is used and is passed through thefour holes in the acrylic sheet. This method of construction correspondsto the normal installation of a transparent noise barrier. The side ofthe sheet had been provided with a rubber profile. The arrangement ofthe steel cables was horizontal.

The weight which impacts the acrylic sheet from a height of 2.64 m wasused to break the sheet. However, it was significant that the impactercould not continue its swing past the retainer, but was retained.

Comparative Example 1

Example 1 was substantially repeated. Although the steel cables used hadthe same mechanical properties, they had no polyamide sheath.

In the pendulum test, the pendulum continued its swing, and this acrylicsheet was therefore not capable of serving as a retaining system.

1-17 (Canceled).
 18. A sound-deadening retention system comprising: atleast one transparent acrylic sheet that comprises at least one embeddedmetal cable; and a synthetic polymer layer between a surface of themetal cable and the transparent acrylic matrix, at least in part.
 19. Aretention system according to claim 18, wherein the synthetic polymerlayer is incompatible with the acrylic matrix of the sheet.
 20. Aretention system according to claim 19, wherein the synthetic polymerlayer is composed of polyamide, polyester, and/or polypropylene.
 21. Aretention system according to claim 18, wherein a thickness of thesynthetic polymer layer is in a range from 50 μm to 1 mm.
 22. Aretention system according to claim 18, wherein the metal cable has anultimate tensile strength in a range from 1,000 N to 100,000 N.
 23. Aretention system according to claim 18, wherein the metal cable has amodulus of elasticity in a range from 50,000 N/mm² to 1,000,000 N/mm².24. A retention system according to claim 18, wherein the metal cablehas a diameter in a range from 0.6 mm to 3 mm.
 25. A retention systemaccording to claim 18, wherein the metal cable comprises iron.
 26. Aretention system according to claim 24, wherein the metal cable iscomposed of steel.
 27. A retention system according to claim 18, whereinthe metal cable is a monofilament.
 28. A retention system according toclaim 18, wherein the metal cable is a polyfilament.
 29. A retentionsystem according to claim 18, wherein the synthetic polymer layer hasbeen applied to the metal cable.
 30. A retention system according toclaim 18, wherein the synthetic polymer layer covers at least 80% of asurface of the metal cable.
 31. A retention system according to claim18, wherein the acrylic sheet comprises a plurality of metal cablesarranged parallel to one another.
 32. A retention system according toclaim 18, wherein the acrylic sheet also encompasses threads composed ofsynthetic polymer.
 33. A retention system according to claim 31, whereinthe metal cables are composed of synthetic polymer and the metal cablesform an angle in a range from 45° to 90°.
 34. Use of a retention systemaccording to claim 18 as a noise barrier.